Plants and nitrogen Plants need nitrogen to grow

Plants and nitrogen • Plants need nitrogen to grow. • It’s present in DNA, RNA, the amino acids that make up proteins, ATP, chlorophyll and most vitamins. • The air is 78% nitrogen gas • BUT nitrogen gas CANNOT be taken up by plants – it is insoluble so cannot be absorbed • So the nitrogen cycle is essential to enable plants to get nitrogen in a form they CAN absorb

How can plants obtain nitrogen? • 2 ways: – Nitrification – Nitrogen fixation • Both require help from bacteria! 1. Nitrifying bacteria 2. Free-living nitrogen-fixing bacteria in the soil 3. Nitrogen-fixing bacteria in root nodules

Nitrifying bacteria • Decomposition by decomposers produces ammonia (NH 3) from the nitrogen in compounds like DNA, proteins etc. • This conversion process is called ammonification. • The ammonia is oxidised by nitrifying bacteria – First to NITRITE (NO 2 -) – Then to NITRATE (NO 3 -) • This process is called NITRIFICATION • Plant roots can absorb the nitrates • These can be combined with carbohydrates from photosynthesis to form amino acids & then proteins & other nitrogen-containing compounds.

Nitrogen-fixing bacteria in root nodules Leguminous plants have root nodules E. g. clover, beans, peas Nodules contain millions of nitrogen-fixing bacteria They have a symbiotic relationship with the plant i. e. both bacteria & plant benefit • They convert nitrogen gas in the soil into ammonia • They do this using an enzyme called nitrogenase • The plant can convert this ammonia directly into amino acids etc. as it is already inside the plant roots • •

Nitrogen-fixing bacteria in root nodules • The reduction of atmospheric nitrogen is a complex process that requires a large input of energy to proceed. • The nitrogen molecule is composed of two nitrogen atoms joined by a triple covalent bond, thus making the molecule highly inert and nonreactive. • Nitrogenase catalyses the breaking of this bond and the addition of three hydrogen atoms to each nitrogen atom. • The plant provides sugars from photosynthesis that are utilized by the nitrogen-fixing bacteria to produce the energy it needs for nitrogen fixation. • In exchange for these carbon sources, the bacteria provide fixed nitrogen to the host plant for its growth.

Free-living nitrogen-fixing bacteria • Free-living nitrogen-fixing bacteria also convert nitrogen gas in the soil into ammonia • These bacteria must find their own source of energy to do this, typically by oxidizing organic molecules released by other organisms or from decomposition. • The bacteria use the ammonia to make amino acids & proteins etc. • When the bacteria die, their proteins decompose, releasing ammonia back into the soil • This ammonia can be converted to nitrates by nitrifying bacteria, & nitrates can be absorbed by the plant roots

BAD bacteria! • Another type of bacteria use nitrates as an energy source and convert them into nitrogen gas • These are DENITRIFYING bacteria • DENITRIFICATION reduces the amount of nitrate in the soil – BAD for plants!

Lightning • The energy from lightning causes nitrogen gas (N 2) and water to combine to form ammonia (NH 3) and nitrates (NO 3). • Precipitation carries these to the ground, where they can be absorbed by plants

NITROGEN GAS (N 2) NITRIFYING BACTERIA NITRITE (NO 2 -) NITRIFYING BACTERIA NITRATE (NO 3 -) DEATH & DECOMPOSITION AMMONIA (NH 3) NITRIFICATION DENITRIFYING BACTERIA DECOMPOSITION (AMMONIFICATION) AMMONIA (NH 3) NITROGEN GAS (N 2) NITROGEN-FIXING BACTERIA IN ROOT NODULES NITROGEN FIXATION FREE-LIVING NITROGEN-FIXING BACTERIA NITROGEN FIXATION

Plants and nitrogen • Plants need ………………. to ……………. • It’s present in DNA, RNA, the ………………. . that make up proteins, ………, chlorophyll and most vitamins. • The air is ………% nitrogen gas • BUT nitrogen gas CANNOT be taken up by plants – it is ………………. . so ………………. be …………………. . • So the …………… is essential to enable plants to get nitrogen in a form they CAN …………. .

How can plants obtain nitrogen? • 2 ways: – ………………………… • Both require help from bacteria! 1. ………………… bacteria 2. Free-living ……………. bacteria in the soil 3. Nitrogen-fixing bacteria in ……………….

Nitrifying bacteria • ………… by decomposers produces ……………. . (NH 3) from the nitrogen in compounds like DNA, proteins etc. • This conversion process is called …………… • The ammonia is …………………. by ………… bacteria – First to ………………… (NO 2 -) – Then to …………………. . (NO 3 -) • This process is called …………. • Plant ……………. . can ……………… the …………………. • These can be combined with carbohydrates from …………… to form amino acids & then proteins & other nitrogen-containing compounds.

Nitrogen-fixing bacteria in root nodules ………… plants have root ………………. E. g. …………………. Nodules contain millions of ……………. . bacteria They have a ………… relationship with the plant i. e. both bacteria & plant benefit • They convert nitrogen ……. . in the ……… into ……………. . • They do this using an enzyme called …………………. . • The plant can ……………. this ammonia directly into …………………. . etc. as it is already ……………… the plant roots • •

Nitrogen-fixing bacteria in root nodules • The reduction of atmospheric nitrogen is a complex process that requires a large input of energy to proceed. • The nitrogen molecule is composed of two nitrogen atoms joined by a triple covalent bond, thus making the molecule highly inert and nonreactive. • Nitrogenase catalyses the breaking of this bond and the addition of three hydrogen atoms to each nitrogen atom. • The plant provides sugars from photosynthesis that are utilized by the nitrogen-fixing bacteria to produce the energy it needs for nitrogen fixation. • In exchange for these carbon sources, the bacteria provide fixed nitrogen to the host plant for its growth.

Free-living nitrogen-fixing bacteria • Free-living nitrogen-fixing bacteria also convert ………………. in the ………. into ………………… • These bacteria must find their own source of …………… to do this, typically by oxidizing organic molecules released by other organisms or from decomposition. • The bacteria use the ………………. to make ………………… & proteins etc. • When the bacteria ……. , their …………………. . , releasing …………………. back into the ………. . • This ammonia can be converted to ……………. . by ………………. bacteria, & nitrates can be ………………. . by the plant …………

BAD bacteria! • Another type of bacteria use ……………. as an ……………. and convert them into nitrogen …… • These are …………… bacteria • ……………. reduces the amount of nitrate in the soil – BAD for plants!